smaller front sprocket causing damage to crank - Honda Motorcycles - FireBlades.org
Honda FireBlade Discussion of the Honda CBR 900RR, Honda CBR 929RR, Honda CBR 954RR, and Honda CBR 1000RR Motorcycles.

User Tag List

Reply
 
LinkBack Thread Tools
post #1 of 33 Old 01-09-2005, 9:34 AM Thread Starter
 
Join Date: 11-17-2004
Posts: 3
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
smaller front sprocket causing damage to crank

I was looking at going down a couple of teeth in the front or up a few teeth in the rear. Ive heard rumors that going down on the front sprocket places extra stress on the crank espeacilly on 929's. I would appreciate anyones help or opinion on this situation.

Last edited by scuba; 01-09-2005 at 9:41 AM. Reason: didnt complete
scuba is offline  
Sponsored Links
Advertisement
 
post #2 of 33 Old 01-09-2005, 12:10 PM
 
Join Date: 12-08-2003
Posts: 168
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

Two less teeth on the front sprocket is a big change in gearing, but it shouldn't hurt the gearbox and definitely won't hurt the crank. It might stress your chain a bit more though because of the reduced diameter of the sprocket. If it was me, I'd go -1 on the front and +3 on the rear sprocket instead (but I still think this is too much personally).
DavidW is offline  
post #3 of 33 Old 01-09-2005, 12:23 PM
 
Join Date: 02-14-2004
Posts: 1,243
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

-2 front could damage the swingarm the chain would probably rub against it a lot. I would go -1 front and the rest on the rear. With stock chain 108 you can go 15 45 wich is almost like 14 43.
l'timbré is offline  
Sponsored Links
Advertisement
 
post #4 of 33 Old 01-09-2005, 12:25 PM
 
Baketech's Avatar
 
Join Date: 02-10-2002
Location: Hoosierland, USA
Posts: 11,098
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 42
                   
Re: smaller front sprocket causing damage to crank

Yes....a smaller front sprocket will add proportionally more overhung load to your countershaft snout and more importantly the bearings...

But there are other more pertinent reasons for not going too small, such as swingarm clearance, increased component wear due to chordal action...yadda, yadda, yadda....

Of course it is all relative, but as a rule of thumb a 15t is the smallest "practical" choice...and even then it's a bit of a compromise....


Edit:
Fixed typo - from "crankshaft" to "countershaft".

Sith Apprentice
CBR929 - VFR800 - VFR800
"There is a grey blur, and a green blur. I try to stay on the grey one..." - Joey Dunlop

Last edited by Baketech; 01-09-2005 at 3:54 PM.
Baketech is offline  
post #5 of 33 Old 01-09-2005, 3:40 PM
 
Rigor's Avatar
 
Join Date: 01-08-2005
Location: PA
Age: 56
Posts: 529
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 15
 
Re: smaller front sprocket causing damage to crank

Coming in on this a little late, but on a previous Yamaha that i owned, i changed from a 15 to a 14 on the front. as stated, keep an eye out for premature wear on the swingarm guard and always make sure your chain is adjusted/maintained correctly.

also, driveline noise becomes more obvious, (especially when driving next to a cement median, or center guardrail) due to the now, tighter, radius the chain has to turn, causing premature chain wear in some cases.
Rigor is offline  
post #6 of 33 Old 01-09-2005, 3:49 PM
 
evl_twn's Avatar
 
Join Date: 07-11-2004
Location: Here
Posts: 1,006
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 23
           
Re: smaller front sprocket causing damage to crank

I don't follow how a reduction in countershaft sprocket size can have any affect on the crankshaft. Perhaps the transmission output shaft/bearing, but how would that cause any harm to the crank? The crankshaft output to the transmission (clutch basket) isn't even on the same side.

I'm sure Honda quality is better, but there was a problem several years ago with the old air cooled Suzuki engines (mostly Katana, but also some GSXR)developing cracks around the output shaft bearing, which was mostly blamed on the chain being adjusted too tight and stressing the cases.
evl_twn is offline  
post #7 of 33 Old 01-09-2005, 3:53 PM
 
Baketech's Avatar
 
Join Date: 02-10-2002
Location: Hoosierland, USA
Posts: 11,098
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 42
                   
Re: smaller front sprocket causing damage to crank

Quote:
Originally Posted by evl_twn
I don't follow how a reduction in countershaft sprocket size can have any affect on the crankshaft. Perhaps the transmission output shaft/bearing, but how would that cause any harm to the crank? The crankshaft output to the transmission (clutch basket) isn't even on the same side.
That was a typo in my post...I meant to say "countershaft snout" instead of crankshaft....fixed it accordingly....

Sith Apprentice
CBR929 - VFR800 - VFR800
"There is a grey blur, and a green blur. I try to stay on the grey one..." - Joey Dunlop
Baketech is offline  
post #8 of 33 Old 02-09-2005, 4:59 PM
 
Join Date: 02-09-2005
Posts: 107
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

Just do it man - youre going to sell the bike one day anyway - or die on it or it will get stolen, so just get on with it !!!!!

Jon
jonno954 is offline  
post #9 of 33 Old 02-09-2005, 5:32 PM
 
Join Date: 05-30-2001
Location: Appleton, WI
Posts: 768
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 25
           
Re: smaller front sprocket causing damage to crank

A friend put a 12 tooth on his Honda 750 back in 1970. It was an old clapped out bike to begin with, but it didn't take long for the chain to break and get shot through the cases.

I'd stick with 15 teeth for efficiency and swingarm clearance.
Zippy is offline  
post #10 of 33 Old 02-09-2005, 6:09 PM
 
Join Date: 05-26-2004
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

Quote:
Originally Posted by DavidW
If it was me, I'd go -1 on the front and +3 on the rear sprocket instead (but I still think this is too much personally).
this is what i'm running right now, and am very pleased with it...still does 85mph at 6.5k

as others have said 14t on the front is probably not so good of an idea, more for chain reasons than crank reasons though...
PrplHaz4 is offline  
post #11 of 33 Old 02-09-2005, 11:22 PM
 
CBRBob's Avatar
 
Join Date: 07-29-2003
Location: Central NJ
Age: 52
Posts: 1,524
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 18
 
Re: smaller front sprocket causing damage to crank

On a bike like the 929/954 andything more than -1f OR +3r is too much if you plan on riding it on the highway.

CBR Bob
TeamPromotion Coach#29TPM
Rider Ed. of N.J. Inc. Senior RiderCoachRENJ
CBRBob is offline  
post #12 of 33 Old 02-10-2005, 1:45 AM
 
Join Date: 08-28-2001
Posts: 3,203
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
       
Re: smaller front sprocket causing damage to crank

Quote:
Originally Posted by Baketech
Yes....a smaller front sprocket will add proportionally more overhung load to your countershaft snout and more importantly the bearings...
Any Mechanical engineers in the house that can explaine this?... I dont see how shortening the leverage arm off a rotating mass attached to a driven shaft is going to change the load on the shaft. The shaft is getting the same amount of power from the engine side. I do understand more leverage being asserted on the chain, and its increased travel speed...but not the shaft itself. Or are we talking about increasing the load on the outer bearing, the one closest to the sprocket?
G-Force Junkie is offline  
post #13 of 33 Old 02-10-2005, 11:25 AM
 
Join Date: 02-09-2005
Posts: 107
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

the wear occurs on the chain, then the chain breaks. That will be bad maintenance. If you wanna mod the thing the you have to look after it. No extra wear will occur on the shaft - thats crap, however making the front smaller will kill the chain.
jonno954 is offline  
post #14 of 33 Old 02-10-2005, 12:07 PM
 
Baketech's Avatar
 
Join Date: 02-10-2002
Location: Hoosierland, USA
Posts: 11,098
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 42
                   
Re: smaller front sprocket causing damage to crank

Quote:
Originally Posted by G-Force Junkie
Any Mechanical engineers in the house that can explaine this?... I dont see how shortening the leverage arm off a rotating mass attached to a driven shaft is going to change the load on the shaft. The shaft is getting the same amount of power from the engine side. I do understand more leverage being asserted on the chain, and its increased travel speed...but not the shaft itself. Or are we talking about increasing the load on the outer bearing, the one closest to the sprocket?
Sure....

T=F*d
-or-
Torque = Force x Distance

In this case:
1. Force = Tension in the chain
2. Distance is equal to 1/2(Pitch Diameter) of the sprocket.
For a 15t this = 1.50"
For a 16t this = 1.60"

Let's assume an output torque of 80lb*ft to make the math easy.
80lb*ft = 960lb*in

From T=F*d:
For a 15t (1.5"), F = 640lbs.
For a 16t (1.6"), F = 600lbs.

This is the resultant chain tension....and the difference in numbers is due to the smaller pitch diameter (ie more leverage). It's also why you feel more "squirt" when riding.

The Force "F" (chain tension) acts on the countershaft, creating a proportionally larger load on the output bearing, and in addition a larger moment in the shaft itself.

*I want to reiterate, that all things are relative. Within reason the higher loads created by a smaller sprocket fit within the design parameters of the drive. But it should be noted that the difference is real, and does have an effect on longevity and wear.

Sith Apprentice
CBR929 - VFR800 - VFR800
"There is a grey blur, and a green blur. I try to stay on the grey one..." - Joey Dunlop
Baketech is offline  
post #15 of 33 Old 02-10-2005, 12:12 PM
 
Join Date: 01-07-2005
Posts: 6
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 0
 
Re: smaller front sprocket causing damage to crank

An Engineer's opinonne tooth smaller on the c-shaft sprocket won't cause you any problems with the chain, counter shaft, cases etc. Just watch those full throttle power shifts from 1st to 2nd (@ the track of course) and remember your speedo will now show some really impressive (and incorrect) speeds and mileage. My solution to the speedo inaccuracy is to apply a piece of duct tape over it.........Works every time!
Steve Kratz is offline  
Reply

  Lower Navigation
Go Back   Honda Motorcycles - FireBlades.org > Honda Motorcycle Models > Honda FireBlade

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Honda Motorcycles - FireBlades.org forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
A valid e-mail address is REQUIRED. You will not have access to any site features until you activate your account using the activation e-mail that is sent to this address.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
speedo recalibration with diff front sprocket ndj Honda FireBlade 59 02-15-2012 5:30 PM
Front sprocket 66droptop Honda FireBlade 56 12-26-2004 8:37 AM
Front Sprocket (954)???? Machinist Honda FireBlade 2 07-13-2004 12:46 AM
Front sprocket wiggle??? NineFiftyFour Honda FireBlade 1 05-15-2004 7:04 PM
17T front sprocket? BillAce Honda FireBlade 5 02-24-2004 8:44 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome